A vapour compression system usually comprises a compressor, a condenser, an expansion device and an evaporator arranged along a refrigerant path. Refrigerant flowing in the refrigerant path is alternatingly compressed and expanded, thereby providing either cooling or heating to a volume. In order to utilise the evaporating capacity of the evaporator to the greatest possible extent, it is desirable to control the flow of refrigerant through the evaporator in such a manner that liquid refrigerant is present throughout the evaporator. However, in the case that liquid refrigerant is allowed to pass through the evaporator there is a risk that this liquid refrigerant may reach the compressor. This may cause damage to the compressor and is therefore undesirable. Accordingly, it is often attempted to operate a vapour compression system in such a manner that liquid refrigerant is present almost through the evaporator. To this end the superheat, i.e. the difference between the temperature of the refrigerant leaving the evaporator and the dew point of the refrigerant leaving the evaporator, is measured, and the supply of refrigerant to the evaporator is controlled in order to obtain a superheat which is small, but positive.
One disadvantage of the control strategy described above is, that the evaporating capacity of the evaporator is not utilised fully, because the superheat of the refrigerant leaving the evaporator must be positive in order to ensure that liquid refrigerant does not reach the compressor. In order to solve this problem an additional, internal heat exchanger may be arranged in the suction line of the vapour compression system, i.e. between the evaporator and the compressor. In this case refrigerant leaving the evaporator is heated in the internal heat exchanger. Thus, in the case that a small amount of liquid refrigerant leaves the evaporator, it is evaporated in the internal heat exchanger. Thereby liquid refrigerant can be present throughout the evaporator without risking that liquid refrigerant reaches the compressor.
In A. Tambovtsev et al., “COP improvement by transfer of the superheating into the internal heat exchanger”, International Congress of Refrigeration 2007, Beijing, a refrigeration system is disclosed. The refrigeration system comprises a suction line heat exchanger in which the heat exchanging fluids flow in parallel in order to stabilise the system.